If you have already e-filed, wait until your return is accepted or rejected by IRS / the state.

                -If your return is rejected, correct your information (along with anything else that needs to be corrected) and then re-submit your return.  See  Fix a reject  Under the Personal Info tab,  make sure to check Yes to Someone else can claim me as a dependent on their tax return.  

               -If your return has been accepted- you cannot change the information. Instead, you have to amend a  return.  See instructions below.

IRS does not allow e-file for amendment,  you will need to submit the amendment forms with related supporting documents by mail. (Follow instructions through the step-by-step interview questions in the program)

If your original return generates a refund, you should wait until your original refund arrives before you file your amendment. You can cash your check, but you still should wait until your current tax return is resolved.  Note that if you see " Do Not File" watermark on your Form 1040-X, this means your original return is either still pending or forms are not finalized yet.

To amend, click here:

https://ttlc.intuit.com/replies/5114064

If you have not filed, to get to the deduction for teacher expenses in TurboTax online program:

• Sign in to your account and select Pick up where you left off
• Select tab Deductions and Credits
• Scroll down to Employment Expenses- Teacher (Educator) Expenses, select Start 
• On-screen, Teacher Expenses, select Yes to continue